I think teens can often "catastrophize" and be extremely negative about every little thing because it is the way they manage anxiety and negotiate situations that are new and changing. You say your ds has always been like this, so was he an anxious child perhaps? Or have there been specific events in his life which have been anxiety provoking? Maybe venting about the little things, helps him handle the big stuff?
When being negative, get to vent their feelings and they do it in their "safe" place, with "safe" people and that is you unfortunately op! 
. You may find he is not as negative at school but it is never seen as cool to be super positive or enthusiastic as a teen either. And it is really great that he deals with big problems calmly.
The important thing is not to get drawn in to their negativity, irritating though it is, it's better to let it wash over you if you can. Something that my DD responds to is humour, if I exaggerate her fears wildly, we can sometimes laugh about it. Another useful exercise is to look back with them over the times when they have catastrophized and been anxious before, and you can say "well remember that time when we missed the train and we thought we would miss the school trip and it was going to be a disaster but it worked out ok in the end because of x, y and z" or, "remember that sleepover when you were really anxious and you had a great time?" "Or when your chain came off your bike but X helped you fix it?".
Overall I think it's better just to respond to their negativity with a "that's a shame" or "yes, agree it would be so great if ..." . Don't try and fix their problems for them and don't either dismiss too much, or validate too much but just stick to a middle, balanced line. And remember he is young. He is not a fully grown adult yet. There is time for him to grow and mature! This is what teenage-hood is for! We adults are not the same as we were in our teens, we are far more resilient and less perfectionist with less black and white thinking (hopefully!), and he will be too!
And lastly , praise the positive! Instead of criticising the negativity, ignore it, but every so often focus on an occasion when he deals with something in a positive way and say "I was impressed with how you handled that patiently without complaining".
Another strategy; take him in to situations where he encounters people less fortunate than himself eg homeless shelter, food bank, walking dogs for the elderly (Cinnamon Trust). It's a cliché but it may help him to gain some perspective on his own situation in life.
Tbh, I can get very negative sometimes and I know it is anxiety at the root of it, so I need to take my own advice!